The present invention relates to a belt-type continuously variable transmission having an automatic clutch and to an engine speed control device for an engine rotating a drive shaft via such variable speed transmission.
A belt-type continuously variable transmission having an automatic clutch in a driving variable-diameter V-pulley is known, for example, from British Patent No. 1010822. In the driving variable-diameter V-pulley provided with an automatic clutch, such as is described in this British patent, a movable pulley element is controlled to slide axially by the resilient force of a clutch spring and the centrifugal force applied to a centrifugal weight whereby a frictional contact conical surface of the movable pulley element is brought into contact with, or separated from, an endless V-belt, so that the automatic clutch, consequently, becomes engaged or disengaged. Upon engagement of the clutch, where the movable pulley element comes into contact with the endless V-belt, the frictional contact surface of the movable pulley element instantaneously catches the endless V-belt to violently engage the clutch. As a result, there occurs a large shock upon engagement of the clutch. In the case of applying this belt-type continuously variable transmission to a motorcycle, for example, the "clutch-on" feeling is deteriorated.
Accordingly, it is an object of the present invention to provide a belt-type continuously variable transmission which can solve the above problem by positively generating a slight amount of slippage in the frictional contact surfaces between the movable pulley element of the driving variable-diameter V-pulley and the endless V-belt and between the movable pulley element of the driven variable-diameter V-pulley and the endless V-belt.
Furthermore, a known engine speed control device is designed to control engine speed by opening or closing a throttle and adjusting suction of air flow. When such conventional engine speed control device is applied to an engine rotating the drive shaft of a belt-type, continuously variable, transmission including variable-diameter V-pulleys mounted on the drive shaft and the driven shaft, respectively, and an endless V-belt wound around both V-pulleys, there occurs the following problem. As the power of the engine is transmitted by a frictional force generated between both the V-pulleys and the endless V-belt, there is naturally generated slippage between both the V-pulleys and the endless V-belt. Particularly, when load applied to the driven shaft becomes greater than the power transmitting force, the power cannot be transmitted from the drive shaft to the driven shaft. Such a stall condition continues until the throttle is operated to close. Under the stall condition, the slippage is maximum to cause acceleration of unbalanced wear of the endless V-belt. This problem is serious, particularly when using a so-called belt clutch effecting contact and non-contact between the V-pulley and the V-belt without the provision of a dedicated clutch for transmitting and cutting the power of the engine.
The present invention has been achieved to solve the above problem, and it is an object of the present invention to provide an engine speed control device adapted to prevent the duration of the stall condition for an extended period of time, in addition to an engine speed control device for controlling the engine speed in response to the throttle opening and closing operation.